What are the differences between Boot UEFI and Legacy BIOS

What are the differences between Boot UEFI and Legacy BIOS

We often hear about UEFI boot when we need to boot the PC or install a new operating system. In this post we will analyze what the new UEFI Boot is and how it works and the differences with the old Legacy Bios

What is the UEFI Boot

UEFI  ( acronym  for  Unified Extensible Firmware Interface ) is the default firmware  interface  for  PC  that has replaced the BIOS environment  . However, as of 2017, the majority of UEFI firmware are also  backwards compatible  with previous BIOS technology ( legacy ).

It supports remote control, remote diagnostics, installation of operating systems, or software update even if no operating system resides in the PC.

It is an Intel patent, which imported Microsoft Windows formats and features. It is written in C language, and is available on Itanium (IA-64), x86 (32 and 64 bit), and ARM platforms. The  Unified EFI Forum  is the association of companies that decide on the technical specification of UEFI, and UEFI 2.0 starting from 2006.

EFI  ( Extensible Firmware Interface ), is a technology initially announced only by Intel at the time of the presentation of its IA-64 architecture of the Itanium processor and then presented in a much more consistent way together with Microsoft at the end of 2003. The purpose of UEFI is to gradually replace the old BIOS of the motherboards and after a shy market debut in early 2006 thanks to Apple’s first Intel Core Duo iMacs, it was introduced in volumes only with Intel Core processors with Sandy Bridge architecture, after being joined by another Intel technology that arrived at the end of 2005, iAMT for remote management of systems.

The original technology (EFI) was created by Intel in 2003 and then taken up and developed, since 2005, by the UEFI consortium (Unified EFI Forum).

Around 2010, new computers (not only ordinary PCs but also workstations and servers) have gradually started to be equipped with UEFI or with motherboard firmware upgradeable to BIOS with at least the efi-boot function of   the system. operating as an option.

UEFI allows manufacturers to integrate applications and new features into the motherboard firmware, including tools for diagnosing and restoring data, cryptographic services and power management features. One of the great advantages of UEFI, compared to the old BIOS, is the graphical interface that makes it look like a common software application. This is due to the fact that the limitation of 16-bit commands and with 1 MB of freshly loaded memory has been exceeded. In addition, many management and administration operations previously impossible with BIOS can be performed via the UEFI firmware interface.

In addition, through UEFI applications and operating system independent UEFI drivers, it facilitates the startup procedure and offers a lot of administrative flexibility. With Windows systems (think of the server versions) the only system to partition disks with a capacity greater than 2 TB (for the known limitations of MBR) is to have a motherboard equipped with UEFI firmware (using 64-bit operating systems for bootable volumes).

UEFI makes it easier to manage PCs and servers remotely, thus helping companies reduce maintenance and support costs, and can directly manage network connections to connect to a LAN or the Internet. In this regard, the firmware based on the UEFI standard are equipped with some specific functions for network management and, possibly, also with a Web browser. Furthermore, by passing the MBR and replacing it with the GPT standard, you can partition the disk with only partitions primaries without the need for extended and logical partitions.

The characteristics of the UEFI boot

One of the characteristics of the UEFI boot is the ability to reduce, even drastically, the loading times of the operating system and to support instant boot forms, similarly to what happens with handheld computers. UEFI also has the task of providing the PC firmware with an effective graphic interface, easy to use and capable of supporting the video resolutions allowed by modern graphic cards. In addition to this, UEFI provides a cross-platform boot environment capable of providing the basic services required by operating systems. In fact, UEFI programs are written in much more modern languages ​​than those used to develop BIOSes.

In a sense, UEFI can be considered a small operating system dedicated to presiding over all those operations that occur between the physical turning on of the machine and the launch of the actual operating system, overcoming all the problems that have emerged over the years with the current BIOS . As such, in fact, it is able to run high-level applications written through standard programming tools. All this will be made possible by the fact that the UEFI interfaces are supported by C ++ language code, thus definitively banning the difficult assembly code of traditional BIOSes.

For Microsoft (which is part of the UEFI consortium consisting of over 140 companies), in addition to “improving the interoperability of the software and resolving the limitations of the BIOS”, the UEFI firmware has the following advantages:

  • improved security by protecting the process before booting from bootkit-type attacks.
  • higher speed of start-up times and recovery from hibernation.
  • support for drives larger than 2.2 terabytes (TB).
  • support for 64-bit firmware device drivers that the system can use to address more than 17.2 billion bytes (GiB) of memory during startup.
  • possibility to use the BIOS with UEFI hardware.

Although UEFI has already been on the market for some time in recent iMacs, these rely on a proprietary chipset developed by Apple . Intel’s first chipset to support UEFI arrived in early 2007 thanks to the Santa Rosa mobile platform based on the Crestine chipset and the Merom processor, but has not met with the favor of system manufacturers.

Any operating system is installed on any computer, equipped with UEFI technology, will install an EFI partition on the disk that acts as an interface between the firmware and the operating system itself: this partition is in Fat32 format and is located at the beginning of the disk and is required for booting installed operating systems; it should not be confused, however, either with the reserved system partitions (for example that of Windows) or with those of recovery (recovery).

The UEFI setup menu usually allows the startup of non-EFI volumes and / or MBR partitioning: it is necessary to act on the available commands that enable the Bios legacy mode  and disable  secure boot .

How does UEFI work?

UEFI solves the same task by incorporating the drivers into your system, which have unlimited memory and are compatible with the updated forms of hardware on the market. These drivers are then written separately and can be loaded using an external flash drive. The loaded data are processed by its programming interface, then configure the data to ensure compatibility.

How to check if the computer is powered by UEFI or BIOS?

  1. Simultaneously press the Win + Rkey to open the Run dialog .
  2. Type ” MSinfo32” in the empty line and press “Enter”.
  3. A new window will open and click on ” System Information” in the left panel. There is an option called “Bios Mode / BIOS Mode” at the bottom right. Legacy means that it is with the traditional BIOS. UEFI means that the computer is powered by UEFI firmware.

UEFI Boot vs Traditional BIOS

  • The memory factor:The BIOS can boot from drives with a memory of 2.1TB or less and with 3TB drives that become very common a computer with a traditional BIOS will not be able to boot, due to how the Master Boot Record (MBR ) of the legacy BIOS works as MBR uses 32-bit entries and limits to a maximum of 4 memory partitions.
  • UEFI uses the GUID partition table(GPT) which uses 64-bit entries and can have infinite partitions but Windows limits to ‘128’ partitions. It also supports drives with memory greater than 2TB with theoretical maximum support value of 9.4 zettabytes.
  •  Since UEFI has more addressable BIOS space, it allows the system to boot faster with faster hardware initialization for the operating system.
  • SecurityThe biggest advantage of using UEFI over the BIOS is that it has security that is not provided by the BIOS. Secure Boot is a UEFI feature that ensures that no malware interferes with the boot process and that the operating system is clean as a whistle. On Windows this system ensures that pirated copies of boot loaders have not been used.


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